The present invention relates to an exhaust gas purifying apparatus and method in an internal combustion engine in which a plurality of exhaust paths are arranged in parallel, and purifiers purifying exhaust gas are respectively provided in the plurality of exhaust paths.
An exhaust gas purifying apparatus has been conventionally utilized in which purification of exhaust gas is carried out by arranging a catalyst in the exhaust path of the engine. A part of equipment such as V-type engines employs a structure in which a plurality of exhaust paths are arranged in parallel. For example, an exhaust gas purifying apparatus in which a catalyst device is provided in each of a pair of exhaust paths arranged in parallel is disclosed in Japanese Laid-Open Patent Publication No. 50-13718 and Japanese Laid-Open Patent Publication No. 3-281929.
In Japanese Laid-Open Patent Publication No. 11-294145 is disclosed an in-line four cylinder diesel engine. When regenerating the purifying apparatus utilizing the catalyst provided in the exhaust path, a reducing agent is supplied to the purifying apparatus, and control for reducing an exhaust flow rate is executed by lowering the opening degree of an exhaust throttle valve. If the exhaust flow rate is reduced, regeneration efficiency of the purifying apparatus utilizing the catalyst is enhanced (it is possible to reduce the amount of reducing agent). However, in a case where the degree of opening of the exhaust throttle valve is simply lowered, engine output is reduced and torque shock is generated. Accordingly, a compensating countermeasure has been devised so as to increase the amount of a main fuel injection supplied to a combustion chamber of the engine as well as increasing a flow rate of an exhaust gas supplied from an exhaust path to an intake path.
However, in order to reduce the exhaust flow rate, since it is necessary to reduce the amount of fresh air reaching the engine, there is a risk of a deterioration in engine emissions such as an increase in smoke.